1GETSOCKOPT(2)              Linux Programmer's Manual             GETSOCKOPT(2)
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NAME

6       getsockopt, setsockopt - get and set options on sockets
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SYNOPSIS

9       #include <sys/types.h>          /* See NOTES */
10       #include <sys/socket.h>
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12       int getsockopt(int sockfd, int level, int optname,
13                      void *optval, socklen_t *optlen);
14       int setsockopt(int sockfd, int level, int optname,
15                      const void *optval, socklen_t optlen);
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DESCRIPTION

18       getsockopt()   and  setsockopt()  manipulate  options  for  the  socket
19       referred to by the file descriptor sockfd.  Options may exist at multi‐
20       ple  protocol  levels;  they are always present at the uppermost socket
21       level.
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23       When manipulating socket options, the level at which the option resides
24       and the name of the option must be specified.  To manipulate options at
25       the sockets API level, level is specified as SOL_SOCKET.  To manipulate
26       options  at any other level the protocol number of the appropriate pro‐
27       tocol controlling the option is supplied.   For  example,  to  indicate
28       that  an  option is to be interpreted by the TCP protocol, level should
29       be set to the protocol number of TCP; see getprotoent(3).
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31       The arguments optval and optlen are used to access  option  values  for
32       setsockopt().   For  getsockopt()  they  identify a buffer in which the
33       value for the requested option(s) are to  be  returned.   For  getsock‐
34       opt(), optlen is a value-result argument, initially containing the size
35       of the buffer pointed to by optval, and modified on return to  indicate
36       the  actual  size  of  the value returned.  If no option value is to be
37       supplied or returned, optval may be NULL.
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39       Optname and any specified  options  are  passed  uninterpreted  to  the
40       appropriate  protocol  module  for  interpretation.   The  include file
41       <sys/socket.h> contains definitions for socket level options, described
42       below.   Options at other protocol levels vary in format and name; con‐
43       sult the appropriate entries in section 4 of the manual.
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45       Most socket-level options utilize an int argument for optval.  For set‐
46       sockopt(),  the  argument should be nonzero to enable a boolean option,
47       or zero if the option is to be disabled.
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49       For a description of the available socket options see socket(7) and the
50       appropriate protocol man pages.
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RETURN VALUE

53       On  success,  zero is returned.  On error, -1 is returned, and errno is
54       set appropriately.
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ERRORS

57       EBADF     The argument sockfd is not a valid descriptor.
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59       EFAULT    The address pointed to by optval is not in a  valid  part  of
60                 the  process address space.  For getsockopt(), this error may
61                 also be returned if optlen is not in  a  valid  part  of  the
62                 process address space.
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64       EINVAL    optlen invalid in setsockopt().  In some cases this error can
65                 also occur for an invalid value  in  optval  (e.g.,  for  the
66                 IP_ADD_MEMBERSHIP option described in ip(7)).
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68       ENOPROTOOPT
69                 The option is unknown at the level indicated.
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71       ENOTSOCK  The argument sockfd is a file, not a socket.
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CONFORMING TO

74       SVr4,   4.4BSD   (these   system   calls  first  appeared  in  4.2BSD),
75       POSIX.1-2001.
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NOTES

78       POSIX.1-2001 does not require the inclusion of <sys/types.h>, and  this
79       header  file  is not required on Linux.  However, some historical (BSD)
80       implementations required this header file,  and  portable  applications
81       are probably wise to include it.
82
83       The  optlen  argument of getsockopt() and setsockopt() is in reality an
84       int [*] (and this is what 4.x BSD and  libc4  and  libc5  have).   Some
85       POSIX  confusion resulted in the present socklen_t, also used by glibc.
86       See also accept(2).
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BUGS

89       Several of the socket options should be handled at lower levels of  the
90       system.
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SEE ALSO

93       ioctl(2),  socket(2),  getprotoent(3), protocols(5), socket(7), tcp(7),
94       unix(7)
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COLOPHON

97       This page is part of release 3.25 of the Linux  man-pages  project.   A
98       description  of  the project, and information about reporting bugs, can
99       be found at http://www.kernel.org/doc/man-pages/.
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103Linux                             2008-12-03                     GETSOCKOPT(2)
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